A vehicle driving apparatus for driving a vehicle of an electric train or the like uses, as a driving source, an electric motor that is disposed under the floor of the vehicle body and runs the vehicle by transferring the torque of the electric motor to the wheels of the vehicle via gear devices and axles disposed on a chassis. With the increase in the running speed of vehicles, there is a demand for further reduction in the size and weight as well as further increase in the capacity of electric motors.
Conventionally, as an electric motor of this kind, an open type electric motor is disposed in which outside air is drawn in and used as cooling wind. Since outside air containing dust is drawn in an open type electric motor, it is necessary to perform maintenance tasks, such as replacement of filters for preventing taint damage to the electric motor and disassembling of the electric motor for periodical cleaning of internal parts, specific to the open type structure. Meanwhile, with the aim of enhancing comfort, there is a demand for noise reduction in the vehicular environment; and noise reduction of electric motors is an issue of particular concern among the issues regarding open type electric motors.
Thus, in response to the pursuit of less maintenance and the measures for reducing internal and external vehicular noise, totally enclosed electric motors have been developed. Because of its structure, the heat releasing capacity of a totally enclosed electric motor is substantially low as compared to an open type electric motor. Therefore, it is necessary to enhance the cooling efficiency. As an example of a cooling system for a totally enclosed electric motor, an outside air ventilating flue is disposed in the electric motor in isolation with the inside of the electric motor. Then, the outside air is ventilated through the outside air ventilating flue. Because of that, heat exchange occurs between the sealed air circulating inside the electric motor and the outside air flowing through the outside air ventilating flue. As a result, the heat generated inside the electric motor is released to the outside (e.g., see Patent Literature 1).
Patent Literature 1: Japanese Patent Application Laid-open No. 2004-194407
Patent Literature 1: Japanese Patent Application Laid-open No. S58-129194